The present invention relates to a chuck assembly for installation in the main shaft of a cutting metalworking machine to hold the workpiece for processing and, more particularly, to a graduated rotation control chuck assembly, which can be controlled to rotate the workpiece step by step at a fixed angle per step.
FIGS. 1 and 2 show a graduated rotation control chuck assembly 1 according to the prior art. This structure of graduated rotation control chuck assembly 1 uses a retractable holding-down rod 2 and a rotary shaft 3 to hold the workpiece 4, and two piston rods, namely, the first piston rod 5 and the second piston rod 6 to control rotation of the rotary shaft 3 step by step at 45xc2x0 per step. The first piston rod 5 and the second piston rod 6 are reciprocated and alternatively forced against the square shaft body of the rotary shaft 3, causing the workpiece 4 to be rotated step by step at 45xc2x0 per step. This structure of graduated rotation control chuck assembly is functional, however it still has drawbacks. Because the graduated rotation control chuck assembly must have two receiving holes 7;8 to hold the first piston rod 5 and the second piston rod 6 separately, the fabrication of the base of the graduated rotation control chuck assembly is complicated. Because the first piston rod and the second piston rod 6 are set subject to a predetermined contained angle and alternatively reciprocated against the shaft body of the rotary shaft 3, the precision requirement of the component parts of the graduated rotation control chuck assembly 1 is critical. Further, in case the angle per step of the rotary motion of the rotary shaft is to be changed, the geometric cross section of the rotary shaft 3 as well as the contained angle of the piston rods 5;6 must be relatively changed, i.e., the base of the graduated rotation control chuck assembly 1 fits only one particular angle per step rotation requirement.
The present invention has been accomplished to provide a graduated rotation control chuck assembly, which eliminates the aforesaid drawbacks. It is therefore an object of the present invention to provide a base for a graduated rotation control chuck assembly, which is easy to fabrication, and less critical in precision requirement. It is another object of the present invention to provide a base for a graduated rotation control chuck assembly, which fits requirements for different rotary angles. To achieve these and other objects of the present invention, the graduated rotation control chuck assembly comprises a base, the base comprising a workpiece receiving chamber, the workpiece receiving chamber having a first lateral side and a second lateral side opposite to the first lateral side; a holding-down rod mounted in the base inside the first lateral side and aimed at the second lateral side and moved axially in and out of the workpiece receiving chamber; and a graduated rotation control unit, the graduation unit comprising a rotary shaft mounted in the base inside the second lateral side and axially aimed at the holding-down rod, the rotary shaft comprising a first contact portion and a second contact portion, a first piston rod, and a second piston rod, the first piston rod and the second piston rod being axially sleeved one inside the other and mounted in the base; wherein the first piston rod and the second piston rod are alternatively reciprocated against said first contact portion and second contact portion of the rotary shaft, causing the rotary shaft to be rotated step by step at a fixed angle per step.